Recently, mobile hand-held devices have increased in popularity, resulting in a corresponding increase in various LCD display products for such devices. In addition, due to widespread use of smart end devices, integration of a touch function into smart end devices has become a mainstream demand for current products.
Referring to FIG. 1, a conventional smart end device having a touch-display function activates a touch driver in a display-pause period for touch driving. As shown, FIG. 1 is a waveform schematic diagram of a conventional shift register having a touch display function, where a display panel has multiple scan lines, and a scan driver comprising multi-stage shift register circuits, a clock signal CK, scan signals G(n−1), G(n), and driving voltages Q(n−1), Q(n). In each frame period, the shift register circuits output the scan signals according to the clock signal to enable the corresponding scan lines of the display panel. For example, the shift register circuits may raise the driving voltage Q(n−1) of an internal driving node Q according to the clock signal CK to output the scan signal G(n−1). In a display-pause period, the shift register circuits are disabled and suspended from outputting the display driving signal G(n), and all of the external signals such as the clock signal CK are disabled such that the driving voltage Q(n) of the driving node Q is in a floating state at this time, resulting in leakage of the driving voltage Q(n) of the driving node Q with time. The longer the external signals such as the clock signal CK are disabled, the more serious is the leakage of the driving voltage Q(n). When the display driving is restored, the scan signal G(n−1) has leakage due to the floating of the internal driving node of the display driving circuit in the display-pause period, resulting in failure of the scan signal G(n) restored after the display-pause period to output a desired voltage level, thereby degrading the display quality. In addition, the waveform distortion of the restored scan signal G(n) results in inconsistency between the time of a falling edge of the waveform and the time of a falling edge of scan signals from other stages, causing the mura effect. Moreover, the display-pause period generally occurs at a constant position of the scan lines. Since the driving nodes Q of the previous-stage and next-stage shift register circuits are also in the leakage state due to floating, a gate end of a driving transistor of the driving unit for pulling down the scan signals G(n−1), G(n) of an output end is continuously stressed, such that the threshold voltage of the driving transistor drifts.
Thus, it is desired to develop methods and devices to prevent the driving transistor of the shift register circuits from being stressed for long periods of time, which results in component performance deterioration and thus erroneous output.